The velocity on a solid surface being zero, we cannot directly define streamlines on a solid surface. If "z" is the coordinate normal to the surface then the velocity is proportional to "z" very close to the surface and we can define the limiting streamlines as the limit as z->0 (continuity of the velocity field is assumed). They are also related to skin friction lines which are used to identify points of separation in a 3-D flow. See <a href=http://aerodyn.org/Wings/3dsepar.html>this</a> page and references therein.

Actually this point of view is no longer the current view of separation - a three-dimensional flow does not necessarily possess a nodal point at separation. Also in unsteady flows the separation point is not even situated at the wall. See the recent book by Sychev et al "Asymptotic theory of separated flows" (Cambridge university press).

To obtain the limiting streamlines you simply calculate the surface values of the stress and use the (in) surface components as "velocities" in the calculation of the streamlines.